Draft controls have been designed for use in stovepipes as shown, for example, in U.S. Pat. Nos. 833,404 and 535,562 consisting of a cone made up of two or more sections pivotally mounted to the inner side of the pipe for expansion and contraction, thus to control the draft and economy of combustion. In contrast, the device of this invention is designed to control the velocity of discharge from industrial chimneys or smokestacks and, hence, to control the height of the plume so that dispersement of the solid particles and gases will take place beyond the aerodynamic downwash at the top of the chimney and thereby minimize air pollution. Such apparatus as shown in the aforesaid patents is neither designed to accomplish the foregoing, nor suggests its use for such a purpose.